A sauna bath that accommodates a large number of people at one time is generally called a "high-temperature sauna bath" which uses a red-hot heating body or an overheated steam heating body installed at a corner of a large sauna chamber to heat the chamber to high temperatures of 80-120.degree. C., normally at around 100.degree. C., thus properly heating the users sitting at locations sufficiently remote from the heating body (type A).
In recent years, a home-use small sauna device has been developed and is gradually beginning to be used. This kind of home sauna device normally uses a small far-infrared ray heating device that can be installed in a bathroom. The heating device includes a plurality of heating bodies having a circular heating surface and arranged at the top and bottom of the front surface of a box-like body of the heating device.
Further, another type that improves the heat efficiency of this home sauna device has a vertical duct provided at the back of the heating body-incorporated front surface to draw in heated air from the top of the duct and blow it out from below a chair on which the user is sitting, thereby enclosing the body of the user with hot air (type B).
In the case of the type-A large sauna bath, because the users receive radiant heat from the hot heating device, there are significant differences between the amounts of heat received by the users sitting at the front row and those at the rear. This naturally causes a large difference in the "sauna effect," the refreshing effect that stimulates perspiration and blood circulation to make users feel refreshed.
Because the users receive high-temperature radiant heat, they can stay in the sauna chamber for only a short period of time, from several to 20 minutes. To use this type of sauna bath requires the user to have a basic physical strength, and there are great variations in the sauna effect according to the physical strength of each user. The user who stay in the sauna for a short period cannot obtain a satisfactory sauna effect. Another disadvantage is that because a large space needs to be provided between the heating device and the users, a large chamber is required deteriorating the efficiency of space usage.
In the type-A large sauna bath, the user's body is subjected to high temperatures (for example, 80-120.degree. C.) that are usually not experienced in daily life. Blood pressure is said to rise at high temperatures more than 70.degree. C. and fall at temperatures below 60.degree. C. although there are variations depending on physical strength. Hence, not only is the use of such a high-temperature sauna bath not recommendable for elderly people or persons with weak physical strength, it is dangerous from the viewpoint of health care.
Generally, elderly people often dislike bath and this makes the work of a person taking care of them more laborious. On the contrary, sun-bathing, necessary for people staying in bed, is recommended for many elderly people and sick persons who are in the process of recovering.
Hence, if a sauna device is available which provides temperature conditions close to that of sun-bathing and still stimulates perspiration like the conventional sauna bath, it can make the bathing more readily acceptable for the elderly or sick person by raising body temperature before taking bath. If the body can be dried naturally after bath, during which communication may take place among elderly and sick persons and nursing personnel, this not only is advantageous for elderly people but can greatly lighten the burdens of the nursing personnel.
The type-B home sauna device is a low-temperature sauna device far smaller than the large type-A sauna bath and has the advantage of being able to be installed at a corner of an ordinary home bathroom so that both the bath and the low-temperature sauna can be used.
Because the home sauna device naturally uses a small space, however, it mainly uses radiant heat radiated from the front of the device to heat the body and there are significant temperature differences between the side of the body that receives radiant heat and the opposite side. Hence, to produce the sauna effect uniformly over the entire body, the user must change his or her body orientation with respect to the heating body at appropriate intervals of time. Therefore, this type of home sauna device, though small and easily installable, cannot provide the sauna effect close to that of the large-size sauna bath to the user as he sits in a relaxed attitude for a long period.
The type-A large high-temperature sauna device has the drawback that it cannot be recommended to elderly or physically weak persons because of high chamber temperature and still requires a large sauna chamber, which degrades the efficiency of space usage. The type-B small low-temperature home sauna device has the drawback of not being able to transfer heat efficiently to the user's body. The inventor of this invention conducted studies to eliminate these drawbacks.
We have developed a device (type C) in which a heating device having a planar heating body is installed on the ceiling portion to supply and discharge hot air from both sides of the ceiling portion to cause the hot air to flow down in the sauna chamber toward the floor surface thereby efficiently heating the body of the user through heat radiation and through direct thermal transfer by contact of hot air to stimulate perspiration.
Another device similar to this type-C sauna device built into the ceiling is a so-called bathroom ventilating/drying device, which has a fan and a heating body installed in the ceiling of the bathroom to blow hot air from the ceiling into the bathroom to heat the interior of the bathroom or which simply exhausts air from the bathroom to use it as a drying compartment. This type of device has found a growing use in newly built condominiums (type D).
The bathroom ventilating/drying device of type D, like an ordinary air conditioner embedded in the ceiling, has a small-area heating body and a fan built into the ceiling. Hence, not only is the volume of air that can be supplied not so large, but the supply port and the suction port are arranged too close together. As a result, a so-called "short-circuit phenomenon" results, in which hot air blown out of the supply port is drawn into the suction port before it reaches the middle of the height of the bathroom.
Once the short-circuit phenomenon of hot air takes place, only the heated air near the bathroom ventilating/drying device or the ceiling portion of the bathroom is circulated, causing overheat of the heater, failing to dry the washing completely.
Further, the bathroom ventilating/drying device has a filter such as a net at the suction port, and dirt trapped by the filter grows into a lump with the elapse of time, which may fall into the hot air circulation duct to contact the heater and ignite, starting a fire. Therefore, the bathroom ventilating/drying device currently on the market has a risk of fire.
When the bathroom is used as a drying compartment by exhausting air from the bathroom, a narrow air passage is automatically formed which connects the air supply port at the bottom of the bathroom door and the bathroom ventilating/drying device. Once this air passage is formed, external air cannot be positively blown against the laundry hung in the bathroom, with the result that the laundry fails to be dried even after the exhaust fan has been operated more than half a day.
Measurements of temperatures along the height in the bathroom incorporating the bathroom ventilating/drying device have shown that the floor surface has the lowest temperature in the bathroom while the ceiling portion is kept at high temperature. The bathroom ventilating/drying device can produce only a small heating effect by which the temperature of air in the upper part of the bathroom near the ceiling is slightly raised. It is therefore out of question to use the bathroom as a small home sauna chamber.
Results of many experiments conducted by the inventors of this invention have found that the problem with the conventional sauna device is that it does not utilize the heat transfer by directly blowing hot air to the user's body.
When room-temperature air is heated to temperatures higher than 70.degree. C.--the temperature that produces the sauna effect, the specific gravity of air decreases by as much as about 30-40%. The lower layer of air that does not reach the temperature at which the sauna effect is produced has a large specific gravity, while the upper layer of heated air is remarkably light.
It is therefore very difficult to blow hot air with a small specific gravity from the ceiling portion and causes it to flow down to or penetrate through an air layer near the floor surface to mix the high-temperature air and the low-temperature air. It is thus impossible to eliminate the large temperature difference that exists between the area close to the ceiling and the area close to the floor. Because the distance between the hot air supply port and the suction port in the bathroom drying device is relatively short, the hot air blown out of the supply port is easily short-circuited to the suction port, failing to heat the whole interior of the bathroom.
The inventor of this invention has long manufactured and marketed this type of sauna device and, based on this experience, developed the present invention by examining the problems with the conventional sauna devices of type A to type D.
It is an object of this invention to provide a sauna device which, though small in size, can produce an excellent sauna effect even for a user not familiar with sauna bath and which enables the user to efficiently use a narrow sauna chamber thereby producing a satisfactory sauna effect even at low temperatures of 40-65.degree. C., preferably at around 50.degree. C.
It is another object of this invention to provide a sauna device which gives the user a large amount of heat in a short period of time.
In the high-temperature sauna device, since the temperature is higher than 70.degree. C., the chamber is extremely dry so that, if water is added, the chamber will necessarily remain dry.
In more concrete terms, the high-temperature sauna device at 100.degree. C. can keep the humidity only at less than 1%, which is abnormally dry. In contrast to this, the low-temperature sauna device at 60.degree. C. can control humidity to 40% at 60.degree. C., 45% at 55.degree. C., 50% at 50.degree. C., 60% at 45.degree. C. and 70% at 40.degree. C.
High humidity in air means that air can hold an increased quantity of heat. As the heat quantity in air increases, the rate of heat transfer to body also increases. The quantity of heat given off to the body increases with the increased rate of heat transfer. This means that the increased heat quantity ensures a satisfactory sauna effect even at low temperatures.
Because a sufficient amount of heat can be imparted to the body through low-temperature air, the user no longer feels direct smarting heat rays on his skin, as experienced in the high-temperature sauna device, and can be warmed down to the core of his body in ways that are pleasant and soft to his body.
The present invention is intended to provide a sauna device that can supply a sufficiently large quantity of heat, even at low temperatures as mentioned above, to the user's body in a short period of time.